DESCRIPTION: The development of T cells involves the differentiation of a common precursor cell into either an alpha/beta (ab) or gamma/delta (gd) lineage T cell, initiating a program of maturation which results in phenotypically and functionally distinct T cells. The overall focus of my project is to examine the pathways and genes governing human ab/gd T cell lineage commitment. First, I will determine the role of T cell receptor (TCR) gene rearrangements in ab/gd lineage commitment using two approaches: a novel quantitative Southern blotting method that I will develop, and PCR-RFLP analysis. I will analyze the rearrangement of b-TCR genes in gd cells and g+d TCR genes in ab T cells and use these data to formulate a model for the role of TCR genes in human ab/gd T cell commitment. Secondly, I will functionally evaluate the lineage potential of discrete populations of cells to become either ab or gd T cells in an in vitro fetal thymic organ culture system. These studies will identify the point of lineage divergence for ab/gd cell development and the phenotypes of the bipotent vs. committed precursors. In summary, my analysis of TCR genes will yield new information regarding the role of T cell receptor rearrangements in the ab/gd lineage decision during human thymopoiesis. Additionally, a functional evaluation of the developmental potential of defined thymocyte populations will pinpoint when lineage commitment occurs, facilitating future cDNA array studies of the gene expression changes happening during this process.